kusahau — to Forget | Swahili Grammar

Kusahau means “forget.” Its stem ends in lexical -u, so it does not follow the native -a → -i/-e alternation: present negative is sisahau, subjunctive is nisahau, and the singular imperative is sahau. The sequence au remains visible throughout the paradigm.

The forgotten content can be a noun, a person indexed by an object marker, an action expressed by an infinitive, or information expressed by a clause. English uses “forget” for all of these too, but the Swahili complement reveals exactly what has failed to remain in memory.

Complete practical paradigm

Form	I	you (sg.)	he/she	we	you (pl.)	they
present	ninasahau	unasahau	anasahau	tunasahau	mnasahau	wanasahau
past	nilisahau	ulisahau	alisahau	tulisahau	mlisahau	walisahau
perfect	nimesahau	umesahau	amesahau	tumesahau	mmesahau	wamesahau
future	nitasahau	utasahau	atasahau	tutasahau	mtasahau	watasahau
present negative	sisahau	husahau	hasahau	hatusahau	hamsahau	hawasahau
past negative	sikusahau	hukusahau	hakusahau	hatukusahau	hamkusahau	hawakusahau
subjunctive	nisahau	usahau	asahau	tusahau	msahau	wasahau

The build ni-na-saha-u gives ninasahau. Unlike kufanya → sifanyi/nifanye, lexical final -u remains in si-saha-u and ni-saha-u. Imperatives are sahau and sahauni; prohibitions are usisahau/msisahau.

Ninasahau majina haraka nisipoyaandika.

I forget names quickly if I do not write them down.

Hawakusahau ahadi yao ya kutusaidia baada ya mafuriko.

They did not forget their promise to help us after the floods.

Usisahau miwani yako unapoondoka nyumbani.

Do not forget your glasses when you leave home.

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Treat final -u as part of the verb, not as the ordinary final-vowel slot. It survives indicative, negative, subjunctive, and imperative forms.

Noun complements and leaving something behind

The forgotten noun follows kusahau as its object.

Nilisahau simu kwenye teksi, lakini dereva aliirudisha.

I left my phone in the taxi, but the driver returned it.

Swahili uses kusahau for both losing something from memory and accidentally leaving it somewhere. The location clarifies the second reading.

Asha amesahau tarehe ya mkutano wa wazazi.

Asha has forgotten the date of the parents' meeting.

Perfect amesahau presents the present result: the date is not accessible to Asha now. Past alisahau simply locates the forgetting in a past narrative.

When an object is already specific and active in discourse, an object marker can index its class.

Kitabu chako nimekisahau ofisini; nitakileta kesho.

I left your book at the office; I will bring it tomorrow.

Ni-me-ki-saha-u contains class 7 -ki- referring to kitabu. A specific human object uses -m-/-wa-:

Sijamsahau mwalimu aliyenisaidia nilipokuwa mtoto.

I have not forgotten the teacher who helped me when I was a child.

This negative perfect uses si-ja-m-saha-u and means “have not forgotten,” often with continuing present relevance.

Infinitive complements: forget to act

An infinitive after kusahau identifies an intended action that was not carried out.

Nimesahau kufunga dirisha la jikoni.

I forgot to close the kitchen window.

Dereva alisahau kujaza mafuta kabla ya safari ndefu.

The driver forgot to refuel before the long journey.

The two verbs remain separate: a-li-saha-u ku-jaz-a. The subject of the infinitive is normally understood as the same person who forgets. This is a linked infinitive, not an object marker or serial tense.

If the intended actor differs, state that participant in a fuller clause rather than forcing the infinitive to carry a new subject.

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Kusahau kufanya means fail to remember to do something. Kusahau kwamba... or kusahau kuwa... means lose track of a fact. The complement type separates prospective action from remembered information.

Clausal content and questions

Nilisahau kwamba duka linafungwa mapema Jumamosi.

I forgot that the shop closes early on Saturday.

Amesahau alipoweka hati ya bima.

She has forgotten where she put the insurance document.

Kwamba introduces a forgotten proposition. An embedded question such as alipoweka... identifies missing information. In (informal) conversation, kuwa may introduce reported content, while kwamba is consistently clear and common in (formal) prose.

Positive commands and collocations

Positive sahau is less frequent than warning usisahau, but it is natural when someone should let go of a concern.

Sahau yaliyopita; tuzungumzie tunachoweza kufanya sasa.

Forget what happened in the past; let us discuss what we can do now.

Common combinations include kusahau jina, kusahau ahadi, kusahau njia, and kusahau kabisa. They are neutral across (informal) and (formal) Standard Swahili.

Forgetting versus not knowing

Kusahau normally implies that the information, object, or obligation was previously available to the forgetter. Kutojua simply denies knowledge and does not imply earlier access.

Nilijua nenosiri hili jana, lakini nimelisahau leo.

I knew this password yesterday, but I have forgotten it today.

Sijui nenosiri la mtandao huu; hakuna mtu aliyeniambia.

I do not know this network's password; nobody told me.

This contrast also explains why a reminder uses causative kukumbusha “remind,” not a causative coined from kusahau.

Nikumbushe nimtumie Amina risiti kabla ya jioni.

Remind me to send Amina the receipt before evening.

In (informal) speech, Nimesahau! can stand alone when the missing item or task is obvious. (Formal) writing usually names the forgotten content so responsibility and timing remain clear.

Common Mistakes

Changing final -u in the present negative

❌ Sisahai majina ya watu.

Incorrect — kusahau keeps lexical final -u.

✅ Sisahau majina ya watu.

I do not forget people's names.

Adding kwa before an infinitive

❌ Alisahau kwa kufunga mlango.

Incorrect for ‘forgot to close’; use a bare infinitive.

✅ Alisahau kufunga mlango.

He forgot to close the door.

Using the wrong object class

❌ Kitabu hiki nimeisahau mezani.

Incorrect agreement — class 7 kitabu does not take class 9 object marker -i-.

✅ Kitabu hiki nimekisahau mezani.

This book, I left it on the table.

Separating the finite verb

❌ Nime sahau namba yako.

Incorrect spelling — finite verb prefixes and stem form one word.

✅ Nimesahau namba yako.

I have forgotten your number.

Key Takeaways

Final -u remains unchanged: ninasahau, sisahau, nisahau, sahau.
A noun complement names what is forgotten; an infinitive names an intended action not performed.
Object markers agree with a specific forgotten noun or person.
Clauses with kwamba and embedded questions express forgotten information.

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